A look inside construction of Seattle tunnel’s double-deck highway

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Q13 News

SEATTLE -- As the tunnel-boring machine Bertha takes a break, the public is getting its first look inside the elaborate construction of the tunnel’s double-deck highway.

Thousands of commuters see the surface construction work along the Alaskan Way Viaduct every day, but what they can't see is 120 feet below downtown Seattle. As Bertha continues to move forward, southbound lanes are being built on the top half of the tunnel. Northbound lanes are being constructed on the bottom half.

After recent delays and sinkhole troubles, the Washington Department of Transportation s now excited to show off its progress with more than 3,000 feet of the State Route 99 tunnel.

WSDOT says its contractor is in the midst of reassessing an anticipated completion date. Bertha has been stopped for routine maintenance for the last three weeks.

Once the digging continues, Bertha will also be installing giant rings that are two-feet concrete segments. Once enough of the tunnel is built, crews will continue the construction of SR 99 under Seattle.

The tunnel includes a flat base and walls built of concrete and reinforced steel. Crews are moving at a rate of 54 feet every two days.

"We're very pleased with the tunneling progress," said Chris Dixon, who works for the contractor,  Seattle Tunnel Partners. "We're especially pleased with how the construction of the interior roadway structure is going."

When the tunnel is complete, it will be one of the longest roadway tunnels in the United States. The amount of concrete in the tunnel is enough to build nine CenturyLink Fields.

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